1. Field of the Invention
The present invention relates to an electronic photographic flash apparatus comprising a DC-DC converter by which a main capacitor is charged with a high tension energy to be fed to a gas-discharge tube, and particularly to an improved constitution provided with a measure to shorten charging time to the main capacitor.
2. Prior Art
A conventional electronic photographic flash apparatus usually takes a considerable seconds from a switching-on of the apparatus to a time when the apparatus becomes ready for flashing with necessary light intensity, and therefore, a first conventional measure that have been taken is closing the power switch sufficiently in advance of a photographing, thereby always charging the main capacitor full in order not to lose a chance of photographing.
A second measure taken for dissolving such inconvenience is a use of a circuit called as series control system wherein a series-connected electronic switching device controls the flashing time period in a manner to cease the flashing when emanated light reaches a necessary amount, thereby shortening the charging time period and also leaving the remaining energy in the main capacitor for the next flashing.
In the abovementioned first measure of switching the apparatus on sufficiently in advance to the instance of photographing leads to a waste of batteries since a DC-DC converter in the apparatus is uselessly working, and therefore the problem is that the batteries must be changed frequently to fresh ones. The second measure, that is the use of the series control system, still has a problem that, the charging-up time can be shortened only for the second flashing or subsequent ones and the charging time for the initial flashing can not be shortened.
Still other measure for shortening the charge-up time was proposed by an invention of the U.S. Pat. No. 4,039,898 or the German Pat. No. 2351389. The proposed apparatus uses a primary battery as a low voltage source and a plural number of secondary batteries, which are connected so as to be charged by the primary battery during waiting time period and then are connected in series each other when operating a DC-DC converter therewith to charge the main capacitor, and thereby providing a multiplied voltage to the DC-DC converter. Though this measure is useful in obtaining a large initial rush current and hence in shortening the initial charging-up time, this circuit has a problem that an ordinary DC-DC converter can not be used since a use of the ordinary DC-DC converter combined with such series-connected secondary batteries will make an over-charging with the rush charging rate to the main capacitor even after a completion of charging a necessary amount of energy.